The present invention relates to building construction technologies. In particular, the present invention relates to the fabrication and installation of reinforcing bars for members of concrete structures, such as columns and walls, among other things. The present invention provides a method and apparatus for the safe, efficient and economical pre-fabrication and erection of assemblies of reinforcing bars used in the construction of concrete structures.
In multi-level concrete construction, it is a common practice to place longitudinal steel reinforcement rods individually. Pre-fabrication of assemblies of longitudinal reinforcing bars is sometimes employed to limit the on-site labor associated with the placement of individual bars. These assemblies generally utilize wire ties or other common bar ties to form an assembly, or module, of typically four or more reinforcing bars. Such assemblies are also often provided with some or all of the transverse reinforcement installed.
Recent advances in concrete reinforcement technology have led to the increased use of threaded reinforcing bars. So-called threadbar reinforcement has continuous thread-like deformations along the length of the bar, and are typically provided with compatible hardware with complimentary internal threading, such as nuts, couplers, anchors, etc. Threadbar reinforcement has been used for many decades and is available from domestic and international suppliers such as Dywidag Systems International, Williams Form Engineering and SAS Stressteel, to name a few.
Threaded reinforcing bars are typically connected with internally threaded couplers. Coupling of the bars generally requires rotating, or spinning, of the couplers along the bars, as well as rotating, or torquing, one or both of the so connected bars for full engagement of the coupler. This requires that one or both of the threaded bars being connected be free to rotate. The use of conventional prefabricated cages, or modules, is generally not suited for this purpose, because in creating a rigid cage for installation, the free rotation of the bars is typically impeded. This represents a significant disadvantage of conventional prefabrication techniques. Another disadvantage of conventional pre-fabricated reinforcement cages is that during their installation the rigging is attached to the permanent cage at the top, thus requiring a worker to climb up the cage to release the hoisting leads.
Alternatively, the prior art patents of Ferrer (U.S. Pat. No. 8,375,678) and Ferrer (U.S. Pat. No. 8,381,479) teach a method and apparatus for the prefabrication of modular reinforcement cages for concrete structures, wherein longitudinal threaded reinforcing bars are held in formation by a set of flat, two dimensional templates with apertures cut at the location and corresponding diameter to the reinforcing bars that are subsequently charged through the apertures. The flat planar templates of Ferrer '678 and Ferrer '479 are provided perpendicular to the axis of the reinforced bars, impeding aggregate material concrete flow therethrough. The apertures are provided with enough clearance from the reinforcing bars to permit free movement of the bars with respect to the template. The reinforcing bars are then locked in place against the template by use of opposing internally threaded lock nuts. Standard set screws are then installed into the lock nuts to provide a temporary locking mechanism to prevent inadvertent rotation, or spinning, of lock nuts during fabrication, transportation and erection. Such locking mechanisms must obviously be removed in order to rotate the bars. The use of internally threaded lock nuts is intended to permit the free rotation of the threaded reinforcing bars through the template and lock nuts, thus allowing the bars to be rotated in the field during installation. The flat, two dimensional templates of Ferrer '678 and Ferrer '479 are intended to provide accurate spatial relation of the longitudinal bars, as well as rigidity for the module when being lifted.
Although the prior art patents of Ferrer '678 and Ferrer '479 are intended to overcome one of the primary disadvantages of conventional pre-fabricated reinforcement cages, they possess certain additional shortcoming and disadvantages, including, but not necessarily limited to:                1. The flat, two dimensional template of Ferrer '678 and '479 occupies a significant sectional area of the concrete element being reinforced, and thus impedes the flow of concrete during placement.        2. The template of Ferrer '678 and '479 occupies a significant sectional area of the concrete element being reinforced and thus also results in a significant discontinuity in the transmission of stress between the concrete on opposite sides of the flat, two dimensional template. This significant discontinuity also facilitates the development of undesirable shrinkage cracks in the concrete.        3. The perpendicular weak-axis orientation of the flat, two dimensional template of Ferrer '678 and '479 with respect to the longitudinal direction of the reinforcement requires a substantial quantity of material to achieve any significant strength and stiffness of the cage.        